Question

How is the presence of $SO_2$ detected?

Answer 1

It is a toxic gas responsible for the smell of burnt matches. $\mathrm{SO}_{2}$ is a colorless and pungent smell gas. So, for detection it is clear that we cannot visibly see the gas but smell the gas.

Complete step- by- step answer:
- By following the below reaction, the presence of $\mathrm{SO}_{2}$ is felt:
$5 \mathrm{SO}_{2}+2 \mathrm{MnO}_{4}+2 \mathrm{H}_{2} \mathrm{O} \rightarrow 5 \mathrm{SO}_{4}+4 \mathrm{H}+\mathrm{SO}_{2}$
- $\mathrm{SO}_{2}$is a gas that also can be detected with the help of $\mathrm{KMnO}_{4}$ solution test in which we pass $\mathrm{SO}_{2}$ through an acidified $\mathrm{KMnO}_{4}$ solution, it does the decolourisation of the test as it help in the reduction of $\mathrm{MnO}_{4}^{- }$ to $\mathrm{Mn}^{2+}$ ions.
- Sulphur dioxide is a very irritating gas and gets easily dissolved in the water and the main constituent of acid rain.
- Sulphur dioxide has an immediate stage for the production of sulphuric acid. It is used for the preservation of fruits,etc.
- It also turns the orange colour of acidic $\mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}$ into green colour as it reduces.

Note: By its colour and smell and its reducing nature, we are able to detect it. Further, this gas reacts easily with any other element to form various kinds of hazardous compounds which can be sulfurous acid, sulphates and also sulphuric acid. The presence of sulphuric dioxide gas results in the discolouration in the reacting compounds or reactions.